Here, we present the concept of flat-field capillary-assisted nanoparticle tracking analysis for the characterization of fast diffusing nano-objects. By combining diffusion confinement and spatially invariant illumination, i.e., flat-fields, within a fiber-interfaced on-chip environment, ultra-long trajectories of fast diffusing objects within large microchannels have been measured via diffraction-limited imaging. Our study discusses the design procedure, explains potential limitations, and experimentally confirms flat-field formation by tracking gold nanospheres. The presented concept enables generating flat-fields in a novel on-chip optofluidic platform for the characterization of individual nano-objects for fundamental light/matter investigations or applications in bioanalytics and nanoscale material science.
